Melissa N., then 23, had been waiting for the right time to break up with her boyfriend of four years when he casually proposed to her back in 2006.

Melissa N., then 23, had been waiting for the right time to break up with her boyfriend of four years when he casually proposed to her back in 2006. It seemed every time she tried to end things with him, her boyfriend would receive some type of bad news ― a health problem would arise or there'd be a family emergency ― that would force her to put it off a bit longer.

"Then on our way to Walmart one day, in my mother's car because we couldn't afford our own, he leaned toward the window and looked at me with one hand on the wheel," Melissa, whose last name has been withheld to protect her privacy, told HuffPost. "He said, 'What do you think, this time next year we'll get married?'"

Melissa was completely shocked ― "but not in a good way."

"I sat quietly for what felt like forever thinking of how embarrassing the situation was and how angry I was that he had asked," she said.

I knew I couldn't spend my life with him. Melissa N.

Melissa asked him if he was serious. He confirmed that he was.

"He said that we'd been together long enough and it was probably about time," she told HuffPost. "I can't remember exactly what I said but it was along the lines of, 'We'll see.' I was panicking on the inside thinking about how I could actually dump him."

Melissa ended the relationship a month later.

"I knew I couldn't spend my life with him," she said.

It's not easy to respond to an unwanted marriage proposal on the spot, particularly one you didn't see coming, as was the case with Melissa. But in an ideal world, the best time to have the conversation with your partner about your feelings on marriage is before the proposal ever goes down.

The worst thing you can do is allow your partner to propose when you know you will turn them down. Amber Harrison

"Proposals can definitely catch a girl or guy off guard but more often than not, the idea of marriage is something you have already discussed," etiquette expert Amber Harrison told HuffPost. "If you believe your partner is planning to get down on one knee ― e.g., you have had conversations about marriage, he has been dropping hints or asking about your ring size ― and you already know you can't accept, then it's time to talk. The worst thing you can do is allow your partner to propose when you know you will turn them down."

If the proposal is sprung on you in front of family and friends, Harrison says, you should not say "yes" in the heat of the moment if you know, in your heart, that your real answer is "no."

"It will be incredibly tempting to say 'yes,'" Harrison told HuffPost. "You will likely feel pressure to appease the waiting crowd and save your partner from any embarrassment. Instead, hug your partner and while you are close, tell them you'd like to speak to them in private. Once you are away from the crowd, you can let them know how you are feeling."

Not feeling ready to accept a marriage proposal right then and there is quite different than knowing you don't want to spend your life with him or her. Anne Chertoff

If your partner pops the question to you in a private setting, you can have a frank conversation about your feelings then and there. Be straightforward but also kind and gracious in your rejection, Anne Chertoff, wedding trend expert at WeddingWire, told HuffPost.

"Be honest about why you are saying 'no.' Is it that you don't ever want to marry? Have the two of you not yet had important conversations about finances, having children, etc., that are making you pause in that very moment?" Chertoff said. "Not feeling ready to accept a marriage proposal right then and there is quite different than knowing you don't want to spend your life with him or her."

These conversations should happen face to face and not over email, text or the phone unless you feel that saying "no" could put your safety in jeopardy.

If you're not currently ready to get married to this person but think you will be down the road, there may still be hope for the relationship. But it depends on the reasons for declining the proposal, Harrison said.

"If you truly believe you want to marry this person but it feels too soon or there are other factors that need to be addressed before you can accept the proposal, then yes, there is absolutely hope for the relationship," she told HuffPost. "If you want the relationship to continue, be sure to communicate that clearly. You will also want to take the time to discuss those things getting in the way of your acceptance."

But do know that the relationship may sour due to the pain of the rejection.

"There is a decent chance that the rejection can be so hurtful to your partner that the hard feelings may never really disappear and it will ultimately be the downfall of the relationship," Harrison added. "Similarly, if you reject a proposal because you really can't see yourself marrying this person, then the relationship will very likely come to an end."